Potentiometers



United States Patent i 3,124,776 POTENTIOMETERS S. Frederic Guggenheim,101 Grayson Place, Teaneck,

N.J.; Hans H. Wormser, 356 Shea Drive, Milford, N.J.;

and Arnold S. Louis, 87 Southgate Ave., Hastings on Hudson, N.Y.

Filed June 16, 1961, Ser. No. 117,730 8 Claims. (Cl. 338174) Thisinvention relates to potentiometers, and more particularly, to thinrotary potentiometers having small external dimensions.

The recent increase in popularity of analogue networks for bothcomputation and control of complex processes has increased the number ofpotentiometers being used. Although the potentiometer is ancient whencompared with most electrical equipment, its use in new environmentspresnets new problems in design and in construction. As the number ofcomponents which are connected together into a network increases, theneed for reducing the size and weight of the individual units alsoincreases. In addition, the recent demand for miniaturization has alsosupplied impetus to the design of smaller potentiometers. In someinstallations, many potentiometers are mounted to be driven by a singleinput device such as a servo motor. One manner in which this isaccomplished is by the passage of a single drive shaft through all of agroup of axially aligned potentiometers whereby, the space required forindividual drives is eliminated and the space between potentiometersusually occupied by driving means from one to the other is saved.Further, the reduction in the size of the potentiometers themselves hasresulted in savings in space and materials.

However, as the size of the potentiometers has decreased, new problemshave been created. The reduction in size of the outside diameters of thepotentiometers also means a reduction in the size of the internalelements, or a rearrangement of the parts to provide the accuracyrequired. In addition, in precision potentiometers such as those used intelemetering, the arrangement of the internal elements must be such asto achieve the desired rotationresistance characteristics. With thedecrease in the size of the internal mechanism, the desired accuracybecomes more diflicult to achieve.

It is an object of this invention to provide a new and improved smallpotentiometer.

Another object of this invention is to provide a new and improvedelectrical contacting arrangement which introduces very little noiseinto the potentimeter output.

A further object of this invention is to provide an improved internalarrangement for a potentiometer take-off, having a greater degree ofreliability than prior take-offs.

Other objects and advantages of this invention will become apparent asthe following description proceeds, which description should beconsidered together with the accompanying drawings in which:

FIG. 1 is a sectional view of a potentiometer arranged to be coaxiallymounted with other such potentiometers;

FIG. 2 is a sectional view of a portion of the potentiometer of FIG. 1;

FIG. 3 is a sectional View of the eyelet and washer assembly of thepotentiometers of FIGS. 1 and 2;

FIG. 4 is a rear view of the assembly of FIG. 2;

FIG. 5 is a sectional view of a potentiometer arranged to be separatelymounted and incorporating the principles of this invention; and

FIG. 6 is a plan view of the brush spring and contact member used in thepotentiometers of FIGS. 1 and 5.

Referring now to the drawings in detail, the reference character 11designates a potentiometer housing made of any suitable constructionmaterial, such as stainless steel,

terminal 28.

3,124,776 Patented Mar. 10, 1964 aluminum, synthetic resin, and thelike. A clamping ring 12 connects the housing 11 with the housing 13 ofan adjacent potentiometer. Within the housing 11, a support member 14 ofelectrical insulating material carries a resistance element 15 formed ofconductive plastic, wire, or a high resistance coating on an insulatingbase. A sliding brush member 16A is carried by spring member 16 whichhas the general shape of the combined brush and spring member shown inFIG. 6. The spring member may be made of beryllium copper or othersuitable spring material. Spring member 16 is carried by shaft 17. Brushmember 16A bears against the top surface of the resistance element 15 tomake a sliding electrical connection therewith. Bearings 18 support theshaft 17 in an end wall of the housing 11 and at other points, notshown, for free rotation. A moving brush block 19 comprising metallicportion 19A and insulator portion 193 suitably bound together ismechanically connected to the shaft 17 for rotation therewith by meansof a set screw 21 or other suitable means. The shaft 17 passes throughan eyelet 23 which supports a washer-like, precious metal contact 24 andserves to attach terminal board 27 to support member 14. The terminalboard also serves as a means for connecting internal terminals 26 andeyelet 23 with external terminals 28 by means of circuitry printed onthe terminal board and shown in FIG. 4. An insulator washer 25 made of adielectric material such as Mylar is confined between flange 35 and araised portion of support piece 14 and prevents short circuiting theinternal terminals 26, and eyelet 23. Terminals 26 are electricallyconnected by conductive parts 33 to the ends of resistive element 15.

It is noteworthy that the above described arrangement of parts 23 and 24separated from terminals 26 by insulator 25 permits these parts tooverlie one another in close proximity. The alternative would be to havethe washer 24 or its equivalent and terminals 26 arranged in concentriccircles on support member 14. This conventional alternative wouldobjectionably increase the diameter of the total assembly. Thearrangement of FIG. 1 permits the design of precision potentiometers,having overall casing diameters as small as /2 inch. These advantagesare particularly important in the design of minia' ture conductiveplastic potentiometers as illustrated.

The manner in which the resistance element, terminal board, and supportmember are connected is better seen in FIG. 2. The eyelet 23, as shownin FIG. 3, comprises a central barrel portion 34, two tabs 31 at one endof the barrel 34, and a flange 35 at the other end of the barrel 34. Theresistance element 15 is molded, or otherwise fastened, to the supportblock 14 so as to form a concentric circular track about a centralperforation in the support block 14. The terminal board 27 also has aperforation, and the barrel portion 34 is inserted through the alignedperforations in the board 27 and the support member 14. When the tabs 31are bent outwardly against the back of the terminal board 27, theassembly is gripped between the flange 35 and the tabs 31, and anelectrical connection is established between some of the circuitry 38 onthe back of the panel board 27 and the flange 35. The washer 24 isfastened to the outside of the flange 35 by any suitable means, such asby soldering or brazing, and, in the completed assembly, is contacted bya portion of sliding brush members 20 carried on either inner arm ofspring member 16 shaped as in FIG. 6. In this manner, an electricalcircuit is formed from an intermediate point on the resistance element15, through the brush contact 16 and the brush spring to the brushcontacts 20, the washer 24, flange 35, barrel 34, tabs 31 to thecircuitry on the terminal board 27 and an external Terminals 26, whichalso act as rivets,

further serve to fasten the board 27 to the support block 14 and connectthe ends of the resistance track 15 to circuitry 38 on the back of theboard 27.

In the assembly of FIG. 1 insulator member 40 surrounds the shaft fromthe brush block of one cup to the brush block of the next. It serves toprevent hi-pot or short circuiting between shaft and activepotentiometer elements such as spring 16 and washer 24. Cover piece 41serves to protect and support board 27 .carrying printed circuit member38. Cover 41 and the entire element assembly are urged in the directionof the brush block by spring 42 so that support piece 14 bears onshoulder 43 in case 11 Case 11 has a milled slot at one side extendingfrom the end of the case to ,the assembled position of the terminalboard 27 and of width to fit the last mentioned part. The elementassembly as shown in FIG. 2 is inserted into case 11 with shaft 17 andbrush block 19 with all attached parts preassembled. Cover piece 41,spring 42 and succeeding case 13 are then assembled. The slot behindterminal board 27 is then filled withclosure piece 44 which is held inplace between clamp 12 and case 13.

An alternative construction for bringing connections to the side of aganged potentiometer is to remove printed circuit board 27 entirely andto attach wires to terminals 26 and tabs 31 and bring these wires out asa cable through the opening in the potentiometer casing otherwiseoccupied by the printed circuit board. The remaining space otherwiseoccupied by the printed circuit board is filled with suitable pottingcompound.

Washer 24and brush member 16 are preferably formed of a noble metal,such asa platinum-palladium alloy, and contact 20 is preferably formedof a gold alloy to maintain contact resistance and noise levels low.

When a potentiometer is constructed for use as a single resistiveelement, terminals are usually provided at its back. Such apotentiometer is illustrated .in section in FIG. and comprises a housing51 having abearing ,52 at one end for rotatably supporting a shaft 53,and ,an end plug 54 of electrically insulating material. Athrust bearing55 carried by the end plug 54 rotatablysupports the other end of shaft53. An insulator brush block 56 is attached to the shaft 53 in asuitable manner such as .by molding thereon, to rotate therewith.Fastened to the brush block 56, such as by a rivet 57, is-a resilientbrush member 58, such as that shown in FIG. 6. The brush member 58comprises a first curved portion 61 and a second curved portion 62having a radius muchsmaller than that of the first portion 61.

A resistance track 59, ,similar to the resistance track of FIGS. 1 and2, issupported on the end plug.5 4 and may be an integral part thereof.A downwardly curved or hooked portion near the end of the first curvedportion 61 of the brush 58 slidably engages the top of the resistancetrack 59 to makeelectrical contact therewith, and dimples near the endsof the second curved por tion 62 of the brush 58 slidably engageawasher-like slipring 63 formed of a low resistance precious metal alloysuch as a gold alloy. A first external terminal 65 extends through theend plug 54 and is electrically connected to the washer 63. Externalterminals .66 (only one of which is shown) also penetrate the end plug54and make electrical connection with the ends of the track 59 by means.of conductive pieces 67. A washer 64 of insulating material insulatesthe under-side of the washercontact 63 from the ends of the terminals66. Terminal 65 and similar dummy .members not shown and not reachingthe outside of the potentiometer also serve as rivets to fasten togetherthe end plug 54 and the washers 63 and 64.

The brush member 58 is better illustrated in FIG. 6 which clearly showsthe first portion 61 having a larger radius than the second portion 62.The ends of both portions are bent downwardly at an angle to the rest ofthe brush member 58 so that the ends bear against the resistance track59 and the washer 63. The brush member 58 is fastened to the brush blockby rivets 57 passing through the holes 68 and 69. Member 58 is made of aprecious metal having spring properties such as a platinum-palladiumalloy. Dimples and curved portions are provided for point contact withthe flat surface of washer 64 and the curved surface of element 59.

As used in the assembly of FIGURE 1, flat beryllium copper spring 16 hasthe general shape of spring 58. Downwardly bent portion .of 61 isreplaced for instance by a half-round piece of precious metal 16A in thesame position and the dimples in 62 are replaced by buttons of preciousmetal which may be molded or soldered to the spring.

In the structure of both FIGS. 1 and 5, the electrical circuitry insidethe casing is completed by usinga washerlike slip-ring made of aprecious metal alloy to provide an electrical connection between oneportion of the brush member and the external terminals There exist,therefore, in each potentiometer casing, two tracks slidably contactedby the ends of the brush member, one track being a resistive element andthe other track having a low resistance. The inner, low resistance trackoverlies the terminal members attached to the outer resistive element.In this manner, the size of the potentiometer may be quite small withoutimpairing the operability of the device. Since the two tracks areessentially concentric, space which is ordinarily wasted in thepotentiometer is utilized to maintain accuracy in a smaller casing.

This specification has described a new and improved potentiometer foruse in precision equipment where small size and weight are important.The structure described comprises a resistive track and a conductivetrack essentially coaxial with each other within the potentiometercasing, and brush means slidably contacting both to establish internalelectrical connections which can be extended outside of the casing. It.isrealized that the above description will indicate to those skilled inthe art other ways in which the invention may be used, and it is,therefore, intended that this invention be limited only by the scope ofthe appended claims.

What is claimed is:

1. A potentiometer comprising a casing, a shaft passing through at leastone end of said casing, a brush member having a first brush portion anda second brush portion mounted on said shaft and electrically connectedto one another, a resistance element mounted on an insulator base withinsaid casing substantially concentric with said shaft, internal terminalmeans for said resistance element mounted on said base and closer tosaid shaft than said resistance element, said resistance element beingpositioned so that it is slidably engaged by said first brush portion, aslip-ring-of high conductance mounted within said casing substantiallyconcentric with said resistance element and positioned to be slidablyengaged by said second brush portion,'said slip-ring overlying saidinternal terminal means in an axial direction with respect to said shaftthe outer diameter of said slip-ring being greater than the distance ofsaid internal terminals from said shaft and less than the internaldiameter of said resistance element, and means for connecting externalterminals to said internal terminal means and said slipfring.

2. The potentiometer defined in claim '1 wherein an insulatormember isinterposed between said slip ring and said internal terminal means.

3. A potentiometer comprising a housing having aligned perforationsthrough its end walls, a shaft passing through said perforations, aresistance element gen erally concentric with said shaft, terminals forsaid resistance element lying closer to said shaft than said element, afirst brush portion mounted on said shaft to be positioned thereby andadapted to contact said resistance element, a second brush portion,mounted on said shaft and electrically connected to said first brushportion, and a slip-ring generally concentric with said shaft andadapted to be connected to external circuitry for said second brushportion, said slip ring overlying said terminals in an axial directionwith respect to said shaft the outer diameter of said slip-ring beinggreater than the distance of said internal terminals from said shaft andless than the internal diameter of said resistance element.

4. The potentiometer defined in claim 3 wherein an insulator member isinterposed between said slip ring and said internal terminals.

5. A potentiometer comprising a generally cylindrical housing havingends, said ends having generally central perforations, a shaft mountedfor rotation in said housing and passing through said perforations, aresistance element generally concentric with said shaft, terminals forsaid resistance element lying between said element and said shaft, abrush assembly mounted on said shaft for rotation therewith, said brushassembly including a first brush portion contacting a surface of saidresistance element, a terminal board for connecting said potentiometerto external circuitry, a member for mechanically coupling said terminalboard and said resistance element, a slipring mounted on said member andelectrically connected to said terminal board, and a second brushportion in said brush assembly adapted to contact said slip-ring, saidslip-ring overlying said terminals in an axial direction with respect tosaid shaft the outer diameter of said slipring being greater than thedistance of said internal terminals from said shaft and less than theinternal diameter of said resistance element.

6. The potentiometer defined in claim 5 wherein an insulator member isinterposed between said slip-ring and said internal terminals.

7. The potentiometer defined in claim 5 wherein said mechanicallyconnecting means comprises a generally cylindrical barrel portion havinga flange at one end and tabs at the other end, said slip-ring beingmounted on said flange.

8. The potentiometer defined in claim 7 wherein an insulator member isinterposed between said slip-ring and said internal terminals.

References Cited in the file of this patent UNITED STATES PATENTS2,145,953 Schellenger Feb. 7, 1939 2,946,032 Daily July 19, 19602,958,840 Barden Nov. 1, 1960

1. A POTENTIOMETER COMPRISING A CASING, A SHAFT PASSING THROUGH AT LEAST ONE END OF SAID CASING, A BRUSH MEMBER HAVING A FIRST BRUSH PORTION AND A SECOND BRUSH PORTION MOUNTED ON SAID SHAFT AND ELECTRICALLY CONNECTED TO ONE ANOTHER, A RESISTANCE ELEMENT MOUNTED ON AN INSULATOR BASE WITHIN SAID CASING SUBSTANTIALLY CONCENTRIC WITH SAID SHAFT, INTERNAL TERMINAL MEANS FOR SAID RESISTANCE ELEMENT MOUNTED ON SAID BASE AND CLOSER TO SAID SHAFT THAN SAID RESISTANCE ELEMENT, SAID RESISTANCE ELEMENT BEING POSITIONED SO THAT IT IS SLIDABLY ENGAGED BY SAID FIRST BRUSH PORTION, A SLIP-RING OF HIGH CONDUCTANCE MOUNTED WITHIN SAID CASING SUBSTANTIALLY CONCENTRIC WITH SAID RESISTANCE ELEMENT AND POSITIONED TO BE SLIDABLY ENGAGED BY SAID SECOND BRUSH PORTION, SAID SLIP-RING OVERLYING SAID INTERNAL TERMINAL MEANS IN AN AXIAL DIRECTION WITH RESPECT TO SAID SHAFT THE OUTER DIAMETER OF SAID SLIP-RING BEING GREATER THAN THE DISTANCE OF SAID INTERNAL TERMINALS FROM SAID SHAFT AND LESS THAN THE INTERNAL DIAMETER OF SAID RESISTANCE ELEMENT, AND MEANS FOR CONNECTING EXTERNAL TERMINALS TO SAID INTERNAL TERMINAL MEANS AND SAID SLIP-RING. 